1. Technical Field
The present invention relates to a semiconductor device, a mounting structure, an electro-optical apparatus, an electronic system, and a method for manufacturing an electronic component including a bump electrode.
2. Related Art
In general, electronic components for semiconductor devices include substrates and bump electrodes disposed thereon. The bump electrodes are attached to mounting boards such that electronic components are electrically connected to the mounting boards. Examples of the bump electrodes include metal bump electrodes that are prepared in such a manner that a thick coating of a metal such as gold (Au) is deposited on each seed electrode portion. Examples of a mounting technique using the bump electrodes include techniques for mounting driving integrated circuits on substrates for various displays.
For example, JP-A-2005-136402 (hereinafter referred to as Patent Document 1) discloses a bump electrode that includes a resin bump disposed on a substrate and a conductive layer disposed on the resin bump. The conductive layer has a smaller thickness as compared to the metal coatings of the metal bump electrodes. This allows fine patterns to be formed, resulting in a reduction in the pitch between electrodes. The bump electrode has an advantage that the elastic distortion of the resin bump is effective in creating a stable contact pressure and therefore high electric reliability can be achieved.
As disclosed in Patent Document 1, the conductive layer has a multilayer structure consisting of a first conductive sublayer (base sublayer) which is made of, for example, a titanium-tungsten (Ti—W) alloy and which is disposed on the resin bump and a second conductive sublayer (conductive surface sublayer) made of, for example, Au. The multilayer structure is useful in that the first conductive sublayer is tightly bonded to the resin bump and the second conductive sublayer protects the bump electrode from corrosion and has good electric contact properties.
However, the bump electrode has a problem that a mounting portion has non-uniform or large contact resistance or contact defects. This is because the first conductive sublayer has ductility lower than that of the second conductive sublayer and therefore cracks when the bump electrode is distorted during mounting, which can cause cracks in the second conductive sublayer.